The present disclosure relates to a fusing device for fusing a toner image to paper, an image forming apparatus incorporating a fusing device, and a method of controlling fusing pressure in a fusing device.
An image forming apparatus that prints with toner is provided with a fusing device for fusing toner transferred to paper. The fusing device is provided with a heating rotary member and a pressing rotary member, and paper having a toner image transferred thereon is passed through a nip between the heating rotary member and the pressing rotary member. This permits the toner image on the paper to be fused to the paper. When the main power to the image forming apparatus is turned on, or when a recovery is made from a power-save mode, a heater provided in the fusing device is energized to perform fusing warm-up operation whereby the heating rotary member is heated to a temperature adequate for fusing. Here, the heating rotary member is in contact with the pressing rotary member, and thus the heat of the heating rotary member is absorbed by the pressing rotary member. As a result, when the first page after fusing warm-up operation is printed, the heating rotary member may not be hot enough to completely fuse toner, resulting in defective fusing.
As a solution to such defective fusing on the first page after fusing warm-up operation, the following technology has been known. Specifically, according to the technology, an image forming apparatus includes a fusing roller, a pressing roller for pressing recording paper against the fusing roller, a heater for heating the fusing roller, and a temperature adjusting means for controlling the heater based on the output of a temperature sensor to adjust the temperature of the fusing roller, and is further provided with a second fusing temperature adjusting means for adjusting, for fusing on recording paper for the first page in response to the first instruction requesting fusing after start-up, the temperature of the fusing roller at, as a target temperature, a second fusing temperature higher than a first fusing temperature. With this configuration, fusing for the first page after start-up is performed at a temperature higher than the first fusing temperature. It is thereby intended to prevent insufficient heating by the heater resulting from the heat of the fusing roller being absorbed by a component nearby, such as the pressing roller, or by recording paper.
On the other hand, to reduce user waiting times and improve user convenience, there have conventionally been made attempts to reduce the time that elapses after a user operation, such as turning-on of the main power, before output of a print (often referred to as the “first print time”). The first print time can be reduced effectively by reducing the time required by fusing warm-up operation.
Here, to be sure, the conventional technology mentioned above can prevent defective fusing during printing of the first page after fusing warm-up operation. However, for fusing on recording paper for the first page after start-up, the temperature of the fusing roller is set at the second fusing temperature higher than the first fusing temperature. That is, before fusing on paper is started, the temperature of the fusing roller needs to be raised up to the second fusing temperature. Thus, the conventional technology mentioned above requires a longer time for fusing warm-up operation. Inconveniently, this results in a longer first print time.